Touch Panel

ABCD

C

D

A BR1 R2

R3R4

R5

R1 R2

R3R4

R5

A B

C

D

How do you isolate the x,y coordinate?

(x,y) OR (R1,R5)

1. Use the microcontroller to read the resistance between pairs of wires.

2. Use simultaneous equations to calculate the values of individual resistances.

Tri-State Logic

HIGH:

I/O pinOUTPUT, HIGH

LOW:

I/O pinOUTPUT, LOW

HIGH IMPEDANCE:

I/O pinINPUT

To Read Between Two Wires

Digital I/O pin 1

Digital I/O pin 2

Digital I/O pin 3

Digital I/O pin 3

Analogue Inputs1 2 3 4

A

B

C

D To Touch Panel

To Read Between Two Wires

Digital I/O pin 1

Digital I/O pin 2

Digital I/O pin 3

Digital I/O pin 3

READ FROM 31 2 3 4

A

B

C

D

HIGH

LOW

HIGH IMPEDANCE

HIGH IMPEDANCE

PASSES THROUGH R1, R3, R4

To Read Between Two Wires(Pin 1,HIGH) V+

(pin 3,LOW) 0V

100Ω fixed resistor (Rf2)

100Ω fixed resistor (Rf1)

Panel Resistance (Rp)

Analogue 3

A

C

Use Simultaneous Equations

D-A: R1+R3+R5D-B: R2+R3+R5A-B: R2+R1

A-D: R5+R3+R1A-C: R4+R3+R1C-D: R4+R5

(R1,R5)-Isolated coordinates

Too Many Pins!

What Next?

The solution: Serial In Parallel Out Shift Registers

01100011 01100011

Chained Together!

Row Control

Column Control

Matrix Schematic

Benefit: Fewer pins than if connected individually.Problem: Can only have individual control of LEDs

one row at a time.